Same filament voltage (10V) and base, higher mu (~5.3) and higher plate dissipation (100W); often paired with the 211 in audio discussions but electrically distinct
Electrical Specifications
Absolute Maximum
Anode Voltage (max)Plate Voltage (max, CCS)1,250V
Anode Dissipation (max)Plate Dissipation (max, Class A₁)75W
Cathode Current (max)Plate Current (max)175mA
Typical Operating
Anode Voltage (typical)Plate Voltage1,000V
Notes
DHT tube: the thoriated-tungsten filament serves as the cathode; there is no heater-cathode isolation.
The base is physically a Medium Metal-Shell Jumbo 4-Pin Bayonet (RCA basing 4AZ), larger than the standard UX4 used on receiving triodes like the 2A3 and 300B.
Three operating points given in the RCA datasheet for Class A₁ service: Va=750V/Ia=34mA/Pout=5.6W, Va=1000V/Ia=53mA/Pout=12W, and Va=1250V/Ia=60mA/Pout=19.7W.
Pa_max is 75W for Class A₁ AF amplifier/modulator service (CCS). Higher dissipation ratings apply in Class B (100W) and Class C (100W) service.
VT-4C is the JAN military designation for the 211; VT-4B is an earlier military variant.
Requires careful attention to filament supply — AC operation is standard; the RCA datasheet grid voltages are referenced to filament midpoint.
Pin Layout — UX4
1Grid
2Filament (f+)
3Plate (Anode)
4Filament (f-)
Socket-Compatible Tubes ⚠ Not electrically compatible